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From: Florian Weimer <fw@deneb.enyo.de>
Newsgroups: comp.lang.ada
Subject: Re: Should Ada runtime provide special primitives for cryptography?
Date: Wed, 01 Oct 2014 23:07:49 +0200
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Date: 2014-10-01T23:07:49+02:00
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* Natasha Kerensikova:

> However, when actually implementing cryptographic stuff, cleverness from
> compiler and optimizer are often enemies. For example, overwriting a
> buffer with zeroes might be optimized out when the buffer is not
> accessed again.

Pragma Inspection_Point covers this.

> I believe it would not be difficult for a compiler vendor to provide, as
> part of the runtime, a zeroing procedure guaranteed to not be optimized
> away, a (generic) array comparison guaranteed to execute in a constant
> number of operations and/or branches, etc. And such subprograms would be
> difficult to write externally, and the guarantees difficult to make
> without tight compiler integration.

The compiler cannot guarantee constant-time execution, that's a
property that emerges from the combination of the object code and the
execution environment (or not).